Parts of the UK are braced for up to 50cm of snow, as Storm Emma brings worsening conditions.
A highly unusual red weather warning for snow is in force for south-west England and south Wales until the early hours of Friday.
UK roads, railways and airports have been severely hit by snow for a third day, with thousands of schools shut.
Thousands of drivers across the country are stranded in freezing temperatures as police urge people not to travel.
The military has been called in to rescue drivers who have been stuck for several hours on the A31 in Hampshire as police declared it a major incident.
Avon and Somerset police have also declared a major incident over concerns medical staff were unable to get to their place of work.
Police said about 100 vehicles are stuck in snow on the A303 at Ilminster, Somerset, and a rescue operation is under way.
In Dorset, around 100 vehicles are stranded on the A35 near Puddletown and a coach full of elderly passengers have been stuck on roads in Northumbria for eight hours, police said.
The Met Office has 11 live severe weather warnings for snow, ice and wind in place for the UK. The final warning is in place until 23:55 GMT on Monday.
On Thursday, a seven-year-old girl died after a car crashed into a house in Looe, Cornwall.
In Leeds, a 75-year-old woman was found dead in a snowy street. She was found partially hidden beneath a car in the Farsley area of the city.
Meanwhile, in the south, a 46-year-old man died in a road crash after a collision with a lorry in icy conditions on the A34 near Tot Hill services in Berkshire.
Earlier, a woman gave birth to a baby girl in a car on the roadside in snowy County Durham.
National Grid says there may not be enough gas to meet demand in the UK.
If suppliers cannot provide more gas, industry, large businesses and gas-fired power stations will be asked to use less, but domestic consumers would only be affected as a last resort.
Children in south Wales, southern England and Scotland were off on a snow day on Thursday, as thousands of schools closed.
Several sports fixtures have been disrupted by weather conditions. Four Super League rugby league have been postponed and the Premier League Darts in Exeter has been cancelled.
Meanwhile, an NHS trust in Leeds said the public response had been "wonderful" after it appealed for people with 4x4 cars to drive health workers to visit patients.
A red alert for snow in Scotland - the country's first- has been lifted but an amber alert remains in place.
On Thursday evening, troops were deployed to transport 200 critical care hospital workers to and from their shifts at two hospitals in Edinburgh.
More than 300 people were stranded on a motorway in Scotland in freezing temperatures overnight on Wednesday - some for 20 hours.
Some 15 law courts across Scotland have cancelled trials on Friday while the high winds have blown panels off the roof of the Princess Royal Maternity Hospital in Glasgow.
First Minister Nicola Sturgeon has urged people there not to travel, while Wales' transport secretary has also warned against driving.
Blizzards, biting winds and significant travel disruption are also affecting southern, western and central England, parts of Wales and Northern Ireland.
This is the third day of disruption caused by heavy snowfall, with reports of "near zero visibility" on some roads in Cumbria.
In Devon and Cornwall, police have warned drivers that most minor roads are "impassable".
By early evening the RAC had reported 8,000 breakdowns across the UK with the West Midlands its busiest region.
Meanwhile, hundreds of homes have been left without power across the UK. On Thursday evening Western Power Distribution, which serves the Midlands, Wales and the south west, said 1,300 homes had power cuts, although not all were weather-related.
The problems for travellers may not be over by the end of this evening with Arriva Trains Wales cancelling several of its services and suspending many others on Friday.
Thousands of drivers trying to get home have been stuck for several hours.
On the M27 in Hampshire motorists have been at a standstill for over five hours while police have declared a major incident on the A31 in the New Forest and called on troops to help rescue stranded motorists.
Highways England said efforts are under way to rescue drivers stuck on the M62, which has been partly closed between Rochdale and Huddersfield.
Police forces across the UK have repeatedly told people to only travel if necessary.
Superintendent Mark Pannone from Cumbria Police said the amount of snowfall was abnormal, adding: "This adverse weather is set to be with us for at least the next 48 hours.
"Many roads are hazardous and so I state again, please do not drive unless you absolutely have to."
What is happening with the trains?
Across the UK, more than 20 rail operators are running a reduced service.
In London, Paddington Station was closed for nearly three hours due to severe weather conditions, and in Kent 50 stations are closed.
National Rail is reporting mass disruption in the South East, Scotland, north-west England and the South West.
- Virgin Trains' west coast service to and from Scotland has not been running since mid morning. Trains to Edinburgh are still cancelled and passengers on east coast routes are urged not to travel until Saturday
- Arriva Trains Wales has suspended some services all day on Friday, including trains between Cardiff and Manchester. Some routes are suspended until at least 13:00 while others are running on a reduced timetable
- Heathrow Express services between London Paddington and Heathrow Airport are running less frequently
- East Midlands Trains are unable to run any trains between Nottingham and Skegness
- There are numerous delays and cancellations on the Northern network, with all trains through Huddersfield delayed by up to 50 minutes or cancelled
- ScotRail ran limited services until 19:00 GMT between Edinburgh and Glasgow, Glasgow Central and Kilmarnock and Glasgow Central and Ayr. There will be no trains in the amber warning area during the Friday morning peak
- No CrossCountry services will run in Scotland on Friday
How are the airports affected?
Airports across Britain are being affected by the cold weather, and the knock-on effect of other terminals across the UK and Europe cancelling flights.
- Glasgow Airport: The airport will stay closed for the rest of Thursday. More than 200 passengers spent the night in the terminal
- Edinburgh Airport: The airport will fully close from 18:00 GMT to give staff time to prepare for Friday's conditions
- Dublin Airport: All flights have been suspended until Saturday
- Cardiff Airport: Flybe has cancelled flights after 15:00 GMT due to the red weather warning in south Wales
- East Midlands Airport: The runway has reopened after being closed because of the snow but it warns passengers of cancellations and delays
- Heathrow Airport: Some flights have been cancelled, with short-haul flights to airports including Dublin and Glasgow severely affected
- Gatwick Airport: About 50 of the 350 flights due to depart from the terminal have been cancelled and there are also significant delays to other flights. Customers are advised to check before travelling
- City Airport: There are multiple cancellations and delays at the airport, mainly affecting Irish and internal flights
What is the forecast?
The Met Office says the cold weather could last into next week and possibly the following week.
BBC Weather's Ben Rich predicted "blizzard conditions" by Thursday night across south-west England, Wales and parts of the Midlands.
He said a "biting easterly wind" will make it feel like -11C (12F) in Birmingham and Cardiff - on what is the first day of meteorological spring.
There is potential for up to 50cm (19.6 inches) of snow over parts of Dartmoor and Exmoor, the Met Office added, with up to 20cm (7.8 inches) falling in southern England, Wales and the West Midlands.
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